Two menus, one page

I’m developing a news theme. It will have two menus: one for each topic (all topics, culture, sports, opinion…) and another for the town (all towns, town1, town2, town3…). By default, “all categories” and “all towns” will be selected, thus showing the frontpage with a selection of the latest from all the news. If any of the topics is chosen, e.g., “sports”, the pieces of news will be selected from the chosen topic (“sports”) and “all towns” (because no town has been chosen yet).

Now it comes the tricky part (for me). If now I select one of the towns, say, “town1”, the front page should show news from “sports” and “town1”. That is, the posts to show should be picked from the last topic chosen from menu1 and the last town chosen from menu2.

Also, it would be nice if the two kind of categories could be arranged separated when creating or editing a post, instead of mixing the topics with the towns.